This invention relates to an electrically operated brake assembly and a method of accommodating brake lining wear.
A typical brake system includes a hydraulic actuator in hydraulic communication with a hydraulic fluid reservoir. The hydraulic actuator forces brake pads or brake shoes toward a disk or rotor. The brake pads or brake shoes include a friction material that engages the rotating member creating a frictional contact that in turn results in a desired amount of braking torque.
Contact between the friction material lining the brake pads or shoes creates frictional contact with the drum or rotor that in turn creates the desired amount of braking torque to slow and stop the motor vehicle. Repeated braking operations progressively wear away friction material resulting in a progressively thinner brake lining. As the friction material wears, the distance between the brake lining and the rotor or drum increases. The increase in distance increases the amount of mechanical travel required to engage the brake. Various mechanical devices are known in the art to adjust and accommodate for the wearing of the brake lining. These devices adjust the brake pad or shoe in order to maintain a desired distance from the brake rotor or drum.
In some applications an electromechanical actuator provides at least a portion of the braking torque required to stop the motor vehicle. The electromechanical actuator is typically an electric motor that drives the brake pads or shoes into engagement with the rotor or drum. A sensor or sensors are used to determine the position of the brake lining relative to the rotating member and then accommodate and adjust for that distance to continually place the brake lining at an optimal distance relative to the rotating member.
As appreciated, the addition of such sensors and other devices increases the complexity and cost of any brake assembly. Further, sensors require calibration in order to provide for accurate position information. Additionally, brake assemblies operate in harsh environments of wide ranging temperature variation and exposure to various contaminants.
Accordingly, it is desirable to develop a brake assembly that automatically accommodates brake lining wear without the use of separate sensors.